In the manufacture of certain wet-laid paper products, such as facial tissue, bathroom tissue, or paper towels, the web is conventionally subjected to a creping process in order to give the web desirable textural characteristics, such as softness, bulk, stretch, and absorbency.
In one form of tissuemaking, the wet sheet is dried by means of through-air dryers, whereby hot air is passed through the sheet to dry it. This process preserves the bulk of the sheet and provides improved softness, a much-desired property. The wet sheet is carried to the through dryer by means of a fabric (referred to as a TAD fabric). The TAD fabric has a 3-dimensional character and serves to mold or pattern the wet sheet so that when dry, this pattern remains in the tissue. In order for effective patterning of the sheet to occur, the wet sheet has to be pulled into the fabric by a vacuum molding box. However after the sheet is dry, it must be transferred from the TAD fabric for additional processing.
In the CTAD process the sheet is transferred to a Yankee dryer and creped prior to final winding on the reel as described below. In the UCTAD process the sheet is separated from the fabric and goes directly to the reel. In both processes, the sheet that has previously been intimately molded into the 3-dimensional TAD fabric must be separated from the fabric without damaging the sheet.
TAD fabric release formulations are used to aid in the separation of the sheet from the TAD fabric. They are applied to the fabric, for example by spraying, prior to transfer of the sheet from the forming fabric to the TAD fabric. In addition by providing good transfer, they help to prevent individual fibers from pulling out of the sheet and remaining with the fabric. This keeps the fabric clean and allows optimum drying and molding of the sheet.
Typical creping processes involve the adherence of the sheet to a rotating creping cylinder, such as an apparatus known as a Yankee dryer, and then dislodging the adhered sheet from the cylinder with a doctor blade. The impact of the doctor blade against the web ruptures some of the fiber-to-fiber bonds within the web thereby causing the sheet to wrinkle or pucker.
In order to increase adhesion, a creping adhesive aid may be used to enhance any naturally occurring adhesion that the web may have due to its water content, which will vary widely depending on the extent to which the web has been previously dried. Creping adhesives should also prevent wear of the dryer surface and provide lubrication between the doctor blade and the dryer surface and reduce chemical corrosion, as well as control the extent of creping. A coating that adheres the sheet just tightly enough to the drum will give a good crepe, imparting absorbency and softness with the desired loss of paper strength. If adhesion to the dryer drum is too strong, the sheet may pick or even “plug”, i.e. slip under the doctor blade, and wrap around the dryer drum. If there is not enough adhesion, the sheet will lift off too easily and undergo too little creping. The creping adhesive, generally in an aqueous solution or dispersion form, is usually sprayed onto the surface of the creping cylinder, e.g. the Yankee dryer.
In order to assist in the uniform release of the sheet at the creping blade, a release aid is sprayed onto the cylinder. These aids assist in the uniform release of the tissue sheet at the creping blade, and also lubricate and protect the blade from excessive wear.
Accordingly, there is an ongoing need in the industry for improved formulations to aid in release of the paper sheet from the TAD fabric and from the creping cylinder.